Environment control system for aircraft having interior condensation problem reduction, cabin air quality improvement, fire suppression and fire venting functions

ABSTRACT

An environment control system for a body of an aircraft that provides controlled ventilation of the interior space of an aircraft body, facilitating reduction of volatile organic compounds (VOCs) within cabin air, dehumidifying and reducing moisture condensation and thus corrosion and other moisture related problems within the envelope, allowing increased humidification of cabin air, and allowing suppression of fires within the envelope. The environment control system includes at least a cabin and an envelope. It includes supply means for supplying a flow of dry ventilation air to the aircraft body. An airflow control device is capable of dividing the flow of ventilation air onto an envelope ventilation air stream and a cabin ventilation air stream. An envelope ventilation duct system directs the envelope ventilation air stream into the envelope, and a cabin duct system directs the cabin ventilation air stream into the cabin. An anti-corrosion/sorption treatment is applied to surface subject to condensation in the envelope. A return air control unit is provided for selectively drawing return air from one of the envelope and the cabin. The environment control system can be incorporated into new aircraft construction, or can be installed as a retro-fit into existing aircraft.

TECHNICAL FIELD

The present invention relates to a method and apparatus for controllingthe environment within an enclosed space. More particularly, the presentinvention relates to an environmental control system for providingcontrolled ventilation of the interior space of an aircraft body, suchthat interior condensation and corrosion is reduced, cabin air qualityis improved, the cabin can be humidified to healthy levels withoutincreasing condensation and associated deleterious effects, and envelopefires can be directly suppressed and vented.

BACKGROUND OF THE INVENTION

In the embodiments of the invention described below and illustrated inthe appended drawings, the “body” of an aircraft is comprised entirelywithin the fuselage, and excludes the wings and tail surfaces, as wellas those portions of the nose and tail cones which extend beyond therespective nose and tail pressure bulkheads. However, it will beunderstood that the present invention is equally applicable to otheraircraft geometries (such as, for example flying wing and lifting bodydesigns). Thus in general, and for the purposes of the presentinvention, the “body” of an aircraft will be considered to be thatportion of the aircraft which is pressurized during normal cruisingflight, and within which it is desirable to control the environment inorder to enhance safety and comfort of passengers and crew.

For the purposes of the present invention, the body of an aircraft isconsidered to be divided into a cabin, one or more cargo bays, and anenvelope which surrounds both the cabin and the cargo bay(s). The terms“cabin” and “aircraft cabin” shall be understood to include all portionsof the interior space of the aircraft which may be occupied duringnormal flight operations (i.e. the passenger cabin plus the cockpit) Theterm “envelope” shall be understood to refer to that portion of theaircraft body between the cabin (and any cargo bays), and the exteriorsurface of the pressure shell (including any pressure bulkheads) of theaircraft. In a conventional jet transport aircraft, the envelopetypically comprises inter alia the exterior fuselage skin; nose, tailand wing root pressure bulkheads; insulation blankets; wire bundles;structural members; ductwork and the cabin (and/or cargo bay) liner.

The term “ventilation air” is defined as outside air typicallyintroduced as bleed air from an engine compressor. For the purposes ofthis invention, “ventilation air” shall be understood to be outdoor airbrought into the cabin by any means, for example, engine bleed air,either with or without filtering. “Ventilation air” does not includerecirculation air or cabin air, filtered or otherwise reconditioned,which is supplied back into the interior space of the aircraft. For thepurposes of this invention, “recirculation air” shall be understood tocomprise air drawn from the interior space of the aircraft, possiblyconditioned, and then returned to the cabin.

To facilitate understanding of the present invention, the followingparagraphs present an outline of condensation/corrosion, air quality,and fire problems encountered in typical jet transport aircraft, andconventional measures taken to address such problems.

Moisture Condensation Problems

Aircraft are subjected to sub-zero temperatures (e.g., −50° C.) whenflying at cruising altitudes. While the aircraft skin is slightly warmerthan outside air due to air friction, temperatures behind and within theinsulation blankets (particularly adjacent the skin) cool to 0° C. to−40° C., depending upon flight duration and altitude. When cabin airpasses behind the insulation, it can reach the temperature at which itsmoisture starts to condense (i.e., its dew point). Further coolingbeyond this temperature will result in additional condensation (asliquid water or ice) on the skin and other cold sinks.

Cabin air circulates behind the insulation, drawn through cracks andopenings by pressure differences created when the cabin is depressurizedduring ascent for example, and during flight by stack pressures(buoyancy effect). Stack pressures are created by density differencesbetween the cooler air behind the insulation and the warmer air in frontof the insulation. The density difference creates a slight negativepressure in the envelope (relative to the cabin) near the ceiling of thecabin and a slight positive pressure in the envelope near the floor ofthe cabin.

The effects of this condensation range from a simple nuisance throughincreased operation costs to decreased aircraft life. The more anairplane is used, the greater its occupant density and the lower theventilation rate per person, the higher its potential for condensationproblems. Cases have been reported of water dripping from the cabinpaneling. Wetting of insulation increases thermal conduction and, overtime, adds weight, increasing operating costs. This condensationincreases the potential for electrical failure. It can lead to thegrowth of bacteria and fungi. It causes corrosion, leading to earlierfatigue failure and reduced aircraft life. Some estimates place capitaland maintenance costs attributable to such condensation at up to$100,000 annually for larger, heavily utilized passenger aircraft.

Conventionally, passive measures have been used to cope with theenvelope moisture problem. These include anti-corrosion coatings,drainage systems, and deliberately maintaining cabin humidity well belowAmerican Society of Air-Conditioning Engineers (ASHRAE) Standardrecommended levels.

U.S. Pat. No. 5,386,952 (Nordstrom) teaches a method for preventingmoisture problems by injecting dehumidified cabin air into the envelope.However, the installation of dehumidifiers, as taught by Nordstrom,increases electrical consumption, occupies additional volume, and addsdead weight. Thus in a recently published study (“Controlling NuisanceMoisture in Commercial Airplanes”) Boeing Aircraft Company concludedthat active dehumidification systems, such as those taught by Nordstrom,are not cost-effective, even though they can reduce moisturecondensation within the envelope. Additionally, the dehumidificationsystem taught by Nordstrom is incapable of addressing related cabin airquality issues, as described below.

Cabin Air Quality

Relative humidities above 65 percent which commonly occur in aircraftenvelopes for even relatively low cabin humidities can support microbialgrowth under appropriate temperature conditions. Such growth can includeGram-negative bacteria. yeasts and fungi. Where sludge builds upanaerobic bacteria may grow, producing foul smelling metabolites.Saprophytic microorganisms provide nutriment for Protozoa. Exposure toaerosols and volatile organic compounds (VOCs) from such microbialgrowth can result in allergenic reactions and illness.

The relative humidity of outside air at typical cruising altitudes isfrequently less than 1-2% when heated and pressurized to cabinconditions. Consequently, since cabin air normally is not humidified, onlonger flights some passengers may experience dryness and irritation ofthe skin, eyes and respiratory system, while asthmatics may sufferincidences of bronchoconstriction. High air circulation velocitiescompound this problem. While humidification of the cabin air duringflight would alleviate the “dryness” problem, it would also exacerbatethe potential for microbial growth and damp material off-gassing in theenvelope.

Thus, although it would be of benefit for health purposes to maintainhigher cabin air relative humidities which are within the ASHRAE(American Society of Heating, Refrigerating and Air-ConditioningEngineers) Standard, this is made impracticable by the envelopecondensation problem.

Other air contaminants in aircraft causing sensory irritation and otherhealth effects can originate from ventilation air, passengers,materials, food, envelope anti-corrosion treatments, envelope microbialgrowth, etc. Ventilation air contaminants originate outdoors and withinthe engine (when bleed air is used). Potential contaminant gases andparticulate aerosols include:

combusted, partially combusted and uncombusted hydrocarbons (alkanes,aromatics, polycyclic aromatics, aldehydes, ketones);

deicing fluids;

ozone, possibly ingested during the cruise portion of the flight cycle;and

hydraulic fluids and lubricating oils, possibly originating from sealleakage within the engine.

Gas chromatography/mass spectrometry (GC/MS) head space analyses ofengine lubricating oil (FIG. 9a), jet fuel (FIG. 9b), and hydraulicfluid (FIG. 9c) indicate some of the potential VOCs that might be foundin aircraft ventilation air.

FIG. 8a shows a GC/MS plot of a ventilation air sample taken in a jetpassenger aircraft during the cruise portion of the flight cycle (28000ft and −34° C.) The total concentration was 0.27 mg/m³ at a cabinpressure altitude of approximately 8000 ft. For comparison, ventilationair VOC concentrations for downtown buildings typically are less than athird of this concentration. VOCs identified include 3-methyl pentane,hexane, 3-methyl hexane, toluene, hexanal, xylene, and many C9-C12alkanes. Additional compounds reported by other researchers includeformaldehyde, benzene and ethyl benzene. Many of the compounds in thejet fuel (FIG. 9b) can be seen in this ventilation air sample. The totalVOC (TVOC) concentration was 0.27 mg/m³ at a cabin pressure altitude ofapproximately 8000 ft. Of this some 0.23 mg/m³ could have a petroleum(combustion source). The TVOC concentration is equivalent to a TOCexposure of 0.36 mg/m³ at sea level. In comparison, urban residentialventilation air TVOC concentrations are typically less than one-thirdthis aircraft ventilation air concentration (i.e., <0.03 mg/m³), andbuilding room air TVOC concentrations typically are less than 0.5 mg/m³.One postulate for the high VOC concentrations found in aircraft is thatperiodic incidents of lubricating oil leakage produce aerosols whichenter the ventilation system and progressively coat the interiorsurfaces of the supply ducts. This coating, in turn, could sorb VOC'singested during taxi from the exhaust of other aircraft. These VOC's maysubsequently be released into the cabin during flight.

Contaminated ventilation air increases ventilation rate requirements toachieve any particular space concentration target. For example, aventilation rate with TVOCs=0.36 mg/m³ must be three times higher thanone with TVOCs=0.036 mg/m³ to maintain a room TVOC concentration of 0.5mg/m³.

Cabin air contaminants can originate from materials and, possiblymicrobial growth in the envelope as well as from cabin furnishings, foodand passengers. Contaminants in the envelope enter the cabin when cabinair is circulated behind the insulation drawn there by envelope stackpressures and by decreasing cabin pressures (for example, duringascent).

FIG. 8b shows a GC/MS plot of envelope air in an aircraft parked whenthe temperature in the air space between the skin and insulation wasapproximately 35° C. The total (TVOC) concentration was 22 mg/m³. Ofthis, some 21 mg/m³ had a petroleum source and 0.6 mg/m³ could have hada microbial source. VOCs from one source of these envelope contaminants,an anti-corrosion treatment, is illustrated in FIG. 9e. This head spacesample was taken at −5° C., a temperature representative of thetemperature behind the insulation during the early portions of cruisingflight. This anti-corrosion treatment emitted many of the compounds seenin the envelope and the ventilation air, plus a number of cycloalkanesand aliphatics not seen in the other samples. FIG. 9d shows the headspace GC/MS plot of a general purpose cleaner (2-butanone or methylethyl ketone) used on this aircraft. This compound was also identifiedin the envelope, engine oil, ventilation air and anti-corrosiontreatment samples.

When the envelope is cooled in flight or warmed on the ground, envelopematerial off-gassing and sorption of contaminant gases change. Forexample under ideal conditions, the deposition of VOCs of interestbehind the insulation could increase a hundred-fold for temperaturedecreases over the typical flight cycle temperature range.

Condensation of higher molecular weight compounds at higherconcentrations may occur when the envelope is cooled. For example, themaximum concentration of dodecane (a compound found in the ventilationair and anti-corrosion treatment samples), at −40° C. is 0.26 mg/m³.

One implication of the above is that during the ascent and the earlyportions of the cruise flight cycle while the envelope is stillrelatively warm, envelope VOCs could pose an air quality problem forpassengers. Another implication is that cabin air VOCs will be deposited(sorbed) in the envelope when it is cold, particularly during laterstages of the cruise portion of the flight cycle. For example, bothventilation air VOCs (FIG. 8a) and the cabin cleaner VOC (FIG. 9d) canbe found in the envelope air sample (FIG. 8b).

Some aircraft have high efficiency particulate filters (HEPA) filterswhich will remove human microbial aerosols that enter the circulationsystem. Some have catalytic converters to remove ozone. Very few havesorbent air cleaners to remove ventilation-air and cabin VOCs.

Fire and/or Pyrolysis in the Envelope

In the case of a fire, thermal and electrical insulation systems in theenvelope as well as other materials in the cabin can undergo pyrolysisand burning, generating toxic smoke and combustion products.Conventionally, this problem is addressed by employing fewer combustiblematerials, and using hand-held containers with non-toxic firesuppressants. Currently, insulation is under review in this regard witha prevention program potentially involving more than 12,000 commercialaircraft.

Under any cabin fire emergency, the objective is to exhaust the smokefrom the cabin while suppressing the fire. There is currently no methodin place to directly suppress or extinguish fire and/or pyrolysis withinthe envelope. Nor is there any effective means of preventing smokewithin the envelop from penetrating into the cabin. Furthermore,exhaustion of air from the cabin is usually via grilles at the floor.which undesirably enhances smoke circulation throughout the cabin.

U.S. Pat. No 4,726,426 (Miller) teaches a method of fire extinguishmentin aircraft cabins using ventilation ducts in communication with thecargo fire extinguishment system. However, this system does not addressenvelope fires and/or pyrolysis, or the health and safety problemsassociated with exposing, passengers to potentially lethal combinationsof fire suppressants and their combustion products in combination withfire and smoke.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an environmentcontrol system that overcomes the above-noted deficiencies in the priorart.

It is a further object of the present invention to provide anenvironment control system capable of inhibiting moist cabin air fromcontacting cold surfaces of the envelope, thereby reducing moisturecondensation within the envelope, and associated “rain-in-the-plane”,electrical failures, corrosion, microbial growth, and dead weight.

It is a further object of the present invention to provide anenvironment control system capable of reducing infiltration of smokefrom the envelope into the interior cabin space, thereby increasingpassenger and crew safety during an in-flight fire situation.

It is a further object of the present invention to provide anenvironment control system capable of improving cabin indoor air quality(IAQ) by at least partially removing contaminants from ventilation airprior to entering the cabin.

Accordingly, an aspect of the present invention provides an environmentcontrol system for an aircraft including at least a pressure shell, aninterior space including one or more of a cabin and a cargo hold, anenvelope extending between the interior space and the pressure shell anda liner disposed between the interior space and the envelope. Theenvironment control system comprises an envelope air distribution systemhaving a plurality of nozzles located at spaced intervals and adapted todistribute an envelope air stream within the envelope in such a manneras to at least partially offset stack effect pressures.

Another aspect of the present invention provides an environment controlsystem for an aircraft including at least a pressure shell, an interiorspace including one or more of a cabin and a cargo hold, an envelopeextending between the interior space and the pressure shell and a linerdisposed between the interior space and the envelope. The environmentcontrol system comprises an envelope air distribution system adapted tosupply an envelope air stream to the envelope; and one or moreflow-blockers adapted to at least partially block a flow of air withinthe envelope.

Another aspect of the present invention provides an environment controlsystem for an aircraft including at least a pressure shell, an interiorspace including one or more of a cabin and a cargo hold, an envelopeextending between the interior space and the pressure shell and a linerdisposed between the interior space and the envelope. The environmentcontrol system comprises an envelope air distribution system adapted tosupply an envelope air stream within the envelope; and sealing meansadapted to at least partially seal the liner against leakage of airbetween the interior space and the envelope.

In embodiments of the invention, one or more flow-blockers are provided,and adapted to at least partially block a flow of air within theenvelope. The envelope air distribution system may include a pluralityof nozzles located at spaced intervals and adapted to distribute theenvelope air stream within the envelope in such a manner as to at leastpartially offset stack effect pressures. Sealing means adapted to atleast partially seal the liner against leakage of air between theinterior space and the envelope may be included.

In embodiments of the invention, the envelope air distribution systemmay further include: at least one envelope supply duct; and at least onerespective ventilation air branch line in communication with theenvelope supply duct and one or more respective nozzles.

An insulation blanket may be disposed within the envelope between theliner and the pressure shell. At least one nozzle may be a shell-sidenozzle adapted to inject envelope air between the insulation jacket andthe pressure shell. At least one nozzle may be a cabin-side nozzleadapted to inject envelope air between the insulation jacket and theliner.

In embodiments of the invention, an air supply is adapted to generatethe envelope air stream. The air supply may include an air supply ductadapted to conduct bleed air from a compressor stage of an engine of theaircraft into the body of the aircraft as ventilation air. The airsupply may also include an airflow control device adapted to divide theflow of ventilation air into the envelope air stream and a cabin airstream. An air conditioner pack adapted to cool the ventilation air mayalso be included. The airflow control device may include at least onevalve adapted for controlling the envelope air stream and the cabin airstream to maintain a predetermined pressure difference between the cabinand the envelope.

In embodiments of the invention, a cabin air distribution system isadapted to distribute the cabin air stream within the interior space ofthe aircraft body. The cabin air distribution system may include: an airconditioner communicating with the airflow control device for receivingat least a portion of the cabin air stream, and adapted to condition thecabin air stream to create cabin supply air; and a cabin supply air ductadapted to direct the cabin supply air into the cabin. The airconditioner may be adapted to control the relative humidity of the cabinsupply air, e.g. to maintain a cabin relative humidity level in excessof 20%.

In embodiments of the invention, the sealing means is adapted to limit aleakage area of the cabin liner such that a predetermined pressuredifference between the interior space and the envelope can be maintainedat a predetermined minimum ventilation rate. The minimum ventilationrate may be about 0.55 lbs per passenger or less. The leakage area maybe equivalent to about 73 cm²) per passenger, or less.

In embodiments of the invention, at least one flow blocker is arrangedto reduce stack effect air flows within the envelope. The flow-blockersmay be arranged to divide the envelope into one or more sections. Insuch cases, the envelope air distribution system may be adapted tocontrol envelope ventilation within a section independently of othersections. At least one section may formed by dividing at least a portionof the envelope longitudinally, e.g. to form at least one section withina crown of the envelope. At least one section may be formed by dividingthe envelope laterally, e.g. to form at least one section within acockpit portion of the envelope. At least one section may formed bydividing the envelope both longitudinally and laterally, to form atleast one section within the envelope proximal a food preparation areaof the cabin.

In embodiments of the invention, a return air control unit is capable ofdrawing a return air stream from a selected one of the interior spaceand the envelope The return air control unit may include a housing, afirst opening defined in the housing and in communication with theenvelope, a second opening defined in the housing and in communicationwith the interior space, and a damper capable of selectively closing oneof the first opening and the second opening. An outflow valve may beadapted to divide the return air stream into an exhaust air stream and arecirculation air stream, the exhaust air stream being vented out of theaircraft, and the recirculation air stream being supplied back to thecabin. The recirculation air stream may be supplied to the cabin via anair conditioner.

In embodiments of the invention an anti-corrosion/VOC sorption treatmentis applied to an interior surface of the aircraft structure within theenvelope. The anti-corrosion/VOC sorption treatment may be formulated toprovide acceptable characteristics of: adhesion to metal surfaces;hydrophobic; low flammability; and low off-gassing at typical envelopetemperatures during cruising flight. The anti-corrosion/VOC sorptiontreatment is formulated to: resist solidification within the aircraftenvelope; sorb ventilation air VOCs at typical envelope temperaturesduring cruising flight and desorb said ventilation air VOC's at warmertemperatures substantially without hysteresis.

In embodiments of the invention, a fire suppression system is providedin communication with the envelope air distribution system. The firesuppression system is preferably capable of releasing a flow of chemicalfire suppressant into at least the envelope air distribution system whensmoke or fire is detected in the envelope. The fire suppression systemand the envelope air distribution system may be adapted to cooperate toflood at least a portion of the envelope with the chemical firesuppressant. The fire suppression system may include a container ofchemical fire suppressant, a supply line in communication with thecontainer and the envelope air distribution system for conducting thechemical fire suppressant between the container and the envelope airdistribution system and a valve capable of controlling a flow ofchemical fire suppressant from the container. The chemical firesuppressant may be any one or more of Halon, carbon dioxide, nitrogenand other fire suppressant agents, or mixtures, of these.

A further aspect of the present invention provides a method ofcontrolling the environment within an aircraft including at least apressure shell, an interior space including one or more of a cabin and acargo hold, an envelope extending between the interior space and thepressure shell, and a liner disposed between the interior space and theenvelope, the method comprising a step of distributing an envelope airstream within the envelope through a plurality of nozzles so as to atleast partially offset stack effect pressures.

Another aspect of the present invention provides a method of controllingthe environment within an aircraft body including at least a pressureshell, an interior space including one or more of a cabin and a cargohold, an envelope extending between the interior space and the pressureshell, and a liner disposed between the interior space and the envelope.The method comprises the steps of: distributing an envelope air streamwithin the envelope; and providing one or more flow-blockers within theenvelope and adapted to at least partially block a flow of air withinthe envelope.

Another aspect of the present invention provides a method of controllingthe environment within an aircraft body including at least a pressureshell, an interior space including one or more of a cabin and a cargohold, an envelope extending between the interior space and the pressureshell, and a liner disposed between the interior space and the envelope.The method comprises the steps of: distributing an envelope air streamwithin the envelope; and at least partially sealing the liner againstleakage of air between the envelope and the interior space, such that apredetermined pressure difference between the envelope and the interiorspace can be maintained at a predetermined minimum ventilation rate.

In embodiments of the invention the envelope air stream is distributedwithin the envelope through a plurality of nozzles so as to at leastpartially offset stack effect pressures. At least a portion of theenvelope air stream may be injected into a space between the pressureshell and an insulation jacket. At least a portion of the envelope airstream may be injected into a space between an insulation jacket and theliner.

In embodiments of the invention, a return air stream may be drawn fromselected one of the envelope and the cabin. The return air stream may bedivided into an exhaust air stream and a recirculation air stream, theexhaust air stream being vented from the aircraft and the recirculationair stream being supplied back to the cabin.

In embodiments of the invention, a supply air stream is divided into theenvelope air stream and a cabin air stream. The cabin air stream issupplied to the cabin; and the envelope air stream and the cabin airstream are controlled to maintain a predetermined pressure differencebetween the cabin and the envelope.

In embodiments of the invention the cabin air is humidified, and thehumidified cabin air is supplied to the cabin.

In embodiments of the invention, during a cruising portion of a flightcycle. the predetermined pressure difference is selected such that theenvelope is at a higher pressure than the cabin. In such cases, thereturn air stream may be drawn from the cabin. Similarly, a portion ofthe return air stream can be vented out of the aircraft, and a remainingportion of the return air stream recirculate back into the cabin.

In embodiments of the invention, during a taxi and ascent portion of aflight cycle, the predetermined pressure difference is selected suchthat the envelope is at a lower pressure than the cabin. In such cases,the return air stream can be drawn from the envelope, and substantiallyall of the return air stream may be vented out of the aircraft.

In embodiments of the invention, during an in-flight fire and/orpyrolysis within the envelope or in the cabin, the predeterminedpressure difference is selected such that the envelope is at a lowerpressure than the cabin. In such cases, at least a portion of theenvelope can be flooded with a chemical fire suppressant, and the cabinair stream may include substantially all of the total flow ofventilation air. The return air stream may be drawn from the envelope,and substantially all of the return air stream vented out of theaircraft.

In embodiments of the invention, during ground operations of theaircraft, the return air stream is drawn from the envelope andsubstantially all of the return air stream is vented out of theaircraft. In such cases, the ventilation air stream may be heated toaccelerate volatilization of VOCs and any moisture within the envelope.

The environment control system of the invention can be incorporated intonew aircraft construction, or installed as an upgrade or retrofit in anexisting aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 shows a schematic cross sectional view through the body of anaircraft, showing components of an air handling system in accordancewith an embodiment of the present invention;

FIG. 2 is an enlarged partial cross section illustrating a portion ofthe embodiment of FIG. 1 in greater detail;

FIG. 3 is a schematic diagram illustrating the operation of the presentinvention during normal cruising flight;

FIG. 4 is a schematic diagram illustrating the operation of the presentinvention during taxi and ascent;

FIG. 5 is a schematic diagram illustrating the operation of the presentinvention during descent from cruising altitude and taxi after landing;

FIG. 6 is a schematic diagram illustrating the operation of the presentinvention during ground purging of the system;

FIG. 7 is a schematic diagram illustrating the operation of the presentinvention during an in-flight fire event;

FIG. 8a shows a gas chromatography/mass spectrometry (GC/MS) analysisplot of a ventilation air sample taken in a jet transport aircraftduring flight (Temperature approximately 20° C.);

FIG. 8b shows a gas chromatography/mass spectrometry (GC/MS) analysisplot of an envelope air sample taken in a jet transport aircraft on theground a approximately 35° C.;

FIG. 9a shows a gas chromatography/mass spectrometry (GC/MS) analysisplot of a head space sample of a jet engine lubricating oil at 100° C.;

FIG. 9b shows a gas chromatography/mass spectrometry (GC/MS) analysisplot of a head space sample of a jet fuel at 90° C.;

FIG. 9c shows a gas chromatography/mass spectrometry (GC/MS) analysisplot of a head space sample of an aircraft hydraulic fluid at 90° C.;

FIG. 9d shows a gas chromatography/mass spectrometry (GC/MS) analysisplot of a head space sample of a general purpose cleaner used inaircraft at 90° C.

FIG. 9e shows a gas chromatography/mass spectrometry (GC/MS) analysisplot of a head space sample of an anti-corrosion treatment sprayed onmetal surfaces in the envelope (−5° C.).

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-3, the body 1 of a typical jet transport aircraftis generally divided into upper and lower lobes. FIGS. 1 and 2 show atypical cross section between adjacent ribs. The upper lobe comprisesthat portion of the body (fuselage) 1 that generally extends above thefloor 2 to enclose the cabin 3 (which may in fact have more than onelevel), and is normally occupied by crew and passengers during flight.Conversely, the lower lobe comprises that portion of the body 1 thatgenerally extends below the floor 2, and normally houses cargo bays 4.Both lobes can conveniently be subdivided into port and starboard sides,which will be symmetrical with exceptions such as doors. As may be seenin FIG. 1, the present invention can be used to provide controlledventilation within all four quadrants of the body 1 (upper lobe-portside; upper lobe-starboard side; lower lobe-port side; and lowerlobe-starboard side). For simplicity of description, the followingdiscussion will focus on only one quadrant (upper lobe-port side) of thebody, it being understood that the same provisions can be made (withappropriate substitutions of components) within each of the otherquadrants as desired.

An upper lobe envelope 5 encompasses the components of the body 1between the outer skin 6 and the cabin liner 7. Similarly, a lower lobeenvelope 8 encompasses the components of the body 1 between the outerskin 6 and the cargo bay liner 9. Conventionally, an anti-corrosiontreatment 41 is applied on the interior surface of the skin and onstructural members within the envelope. An insulation blanket 10 isnormally provided within the upper and lower lobe envelopes 5, 8 and istypically secured to the stringers 11, so that a small gap 12 normallyexists between the skin 6 and the outermost surface of the insulation10.

The present invention provides an environment control system whichoperates by controlling flow of air within both the cabin 3 and theupper and lower lobe envelopes 5 and 8. The system comprises an airflowcontrol device 13; upper and lower lobe envelope supply ducts 14P, 14S,15P and 15S which communicate with the airflow control device 13 andwhich run generally parallel to the aircraft longitudinal axis; one ormore ventilation air branch lines 16 which communicate with each of theupper and lower lobe envelope supply ducts 14, 15 and extend into tierespective upper and lower lobe envelopes 5, 8; a plurality of returnair controllers 17 which communicate with a respective main return airduct 18P, 18S; an outflow valve 19 communicating with the main returnair ducts 18; a cabin air conditioner 20; a cabin supply air duct 21;and a control unit 22.

The lower lobe envelope supply ducts 15P and 15S and associatedventilation air branch lines 16 are independent of the main part of thesystem and can be omitted if desired.

Referring now to FIG. 3, dry ventilation air 24, for example air bledfrom the compressor section of an engine 23 in a conventional manner andoptionally conditioned (that is, cooled and possibly dehumidified) byconventional conditioning packs 23 a, is supplied to the airflow controldevice 13. The airflow control device 13 operates in response to controlsignals A from the control unit 22 (or optionally is pre-set) to dividethe flow of ventilation air 24 to create an envelope air stream 25, atleast a portion of which is distributed to the upper lobe port sideenvelope 5 through the port-side upper envelope supply duct 14P andventilation air branch lines 16, and a cabin air stream 26 which issupplied to the cabin air conditioner 20.

In the illustrated embodiment, the airflow control device 13 is providedas a unitary control valve. However, it will be appreciated that theairflow control device 13 may be provided as any suitable combination ofone or more valves; dampers, orifices or duct assemblies, which may beused in combination with conventional ventilation ducts previouslyexisting within an aircraft. Similarly, the ventilation supply duct 14Pmay be a separate air supply duct, or may be a supply air duct such ascabin or gasper ventilation air supply lines, previously installed in anaircraft.

The ventilation air branch lines 16 are distributed at suitableintervals along the length of the upper envelope supply duct 14P so asto provide a distribution of envelope air 25 alone the length of theupper lobe envelope 5. The number of ventilation air branch lines 16will, in general, depend on the tightness of the envelope (i.e. leakagebetween cabin and envelope) and the presence of air-flow obstructionswithin the envelope. In aircraft with a particularly tight cabin linerand few obstructions to longitudinal flow within the envelope, as few asone ventilation air branch line 16 may be used. In other situations, agreater number of ventilation air branch lines 16 may be preferredConveniently, a single ventilation air branch line 16 can be provided ineach rib space of the body 1. Each ventilation air branch line 16includes a plurality (four are shown in the illustrated embodiment, seeFIG. 1) of shell-side nozzles 27 which are designed to inject envelopeair 25 behind the insulation 10, that is, into the space 12 between theskin 6 and the insulation 10. The shell-side nozzles 27 are distributedat suitable intervals around the circumference of the upper lobeenvelope 5, so that envelope air 25 can be supplied to the envelope 5.behind the insulation 10. The number and spacing of shell-side nozzles27 will depend on the tightness of the cabin liner, and the presence ofobstructions to circumferential movement of air. Preferably, theenvelope air flows are controlled to be sufficient to neutralize stackeffect pressure (of up to 1.5 Pa with a least one flow blocker per side)and create slightly higher pressures in the envelope relative to thecabin (e.g., at least 0.5 Pa).

The “stack effect” is a phenomenon which occurs within the envelope andwhich tends to cause a circumferential flow of air within the envelope.In general envelope air between the insulation 10 and the cabin liner 7tends to rise (because it is lower density); passes through theinsulation 10 where it contacts the fuselage skin 6 and cools; the coldenvelope air between the insulation 10 and the skin 6 tends to sink(because it is higher density), and passes back through the insulation10 near the floor 2 of the cabin 3. The amount of this naturalconvective flow depends on cabin height, the temperature differentialacross the insulation 10, and the presence of flow restrictions. In aconventional aircraft fuselage, stack effect pressures of up toapproximately 3 Pa or more can be encountered at cruising altitudes.

In order to reduce stack effect it is useful to provide at least oneflow blocker 28 within the envelope 5 which serves to blockcircumferential movement of air within the envelope 5. Preferably, aflow blocker 28 is positioned between the panel 7 and the insulation 10,and squeezes the insulation against the skin 6 or stringer 11. In mostconventional jet transport aircraft, a single flow blocker 28 willnormally be sufficient. In such cases, the flow blocker 28 canadvantageously be installed at approximately mid-height within theenvelope 5 (i.e. just above the windows (not shown) on both sides of aconventional jet transport aircraft). This reduces stack effectpressures to approx. 3 Pa or less at cruising altitudes. In very largeaircraft, particularly those with multi-level cabins it may be necessaryto install two or more flow blockers 28 on each side.

Optionally, one or more cabin-side nozzles 29 (two are shown in theembodiment of FIG. 1) can also be provided in order to inject envelopeair 25 into the upper lobe envelope 5 in front of the insulation 10,that is, between the insulation 10 and the cabin liner 7.

When the envelope air 25 is injected behind the insulation 10, theenvelope air 25 will be cooled well below the cabin temperature (forexample, by as much as 60° C., going from +20° C. to −40° C.). Thiscooling, promotes ventilation a contaminant sorption and condensation inthe envelope. In particular, most VOCs identified in cabin air (see FIG.8a) may condense at temperatures well above −40° C. on cold envelopesurfaces (for example the interior surface of the fuselage skin 6 andadjoining structural members), during cruising flight. Particles (e.g.oil aerosol) entrained within the envelope air stream 25 may impact andadhere to the interior surface of the skin (or adjoining surfaces),and/or will be removed (by physical filtration or electrical forces) asthe air passes through the insulation blanket 10 toward the cabin.

It will be noted that any water vapor present in the envelope air 25will also tend to condense on the cold surfaces within the envelope 5.However, because of the extremely low relative humidity of the envelopeair 25, at least during the cruise phase of flight, the amount ofmoisture likely to accumulate within the envelope 5 is negligible.

Sorption of VOC's within the envelope 5 can be enhanced by replacing theconventional anti-corrosion treatment 41 with an improved compositionhaving both anti-corrosive and enhanced VOC sorbent properties. Thecombined anti-corrosion/VOC sorption treatment 41 on the skin andstructural members in the envelope is formulated to: not freeze attemperatures above −50° C.; maximize sorption of typical ventilation airVOCs in the temperature range 0 to −40° C.; and maximize desorption ofthese compounds in the temperature range 10° C. and higher. Aparticularly suitable formulation will be capable of performing multiplesorption/desorption cycles without hysteresis (i.e. it does notgradually become loaded with effectively permanently sorbed VOC's) orchemical degradation. It contains an anti-oxidant that ensures that itwill not harden for several years and so will remain sorbent betweenregular maintenance cycles when it can be renewed.

The envelope air 25, after being cooled, passes through the insulation10 to the cabin liner 7. During this passage, the air is heated by thedynamic insulation effect before it enters the cabin 3. If the envelopeair 25 is injected in front of the insulation 10, contaminant removalthrough sorption and condensation is reduced. However, the envelope 5 isstill pressurized with dry air throughout, preventing humid cabin airentry and thus allowing the cabin 3 to be humidified to desirablelevels. Nozzles placed behind the insulation 10 improve the efficiencyof VOC contaminant removal during flight at cruising altitudes throughsorption and condensation, removal of ozone through surface contact withreactive materials, and deposition of particles through centrifugal andelectrical forces. Nozzles placed in front of the insulation 10 simplifyinstallation and reduce heat loss. Either option, taken alone or incombination, can be utilized as required.

In order to ensure that air passes from the envelope 5 and into thecabin 3, the cabin must be maintained at a slight negative pressurerelative to the envelope. This can be accomplished by drawing return airfrom the cabin 3, by connecting the return air ducts 18 in communicationwith the cabin space, for example via one or more simple return airgrills.

In order to provide enhanced system capability, one or more return aircontrol units 17 are provided at suitable intervals along the length ofbody 1, as shown in FIGS. 1 and 2. The use of such return air controlunits 17 permits return air to be selectively drawn from either thecabin or the envelope, as desired thereby facilitating smoke removal,envelope purging, and fire suppressant injection while maintaining anegative pressure in the envelope relative to the cabin. Conveniently, areturn air control unit 17 can be provided in association withconventional return air ducting, arrangements previously provided withinan existing aircraft. In the illustrated embodiment, a return aircontrol unit 17 is provided in each rib space at the floor level of theupper lobe envelope 5. Each return air control unit 17 comprises ahousing 30 having an envelope opening 31 communicating with the upperlobe envelope 5, and a cabin opening 32 communicating with the cabin 3.A damper 33 within the housing 30 enables a selected one of the envelopeopening 31 and the cabin opening 32 to be opened and the other to beclosed. Thus return air can be selectively drawn from within theenvelope 5 or the cabin 3 as desired and in accordance with theoperating regime of the aircraft. The position of the damper 33 can becontrolled by any suitable drive means (not shown), such as, forexample, a solenoid, servo motor or pneumatic actuator in response tocontrol signals B received from the control unit 22. Each return aircontrol unit 17 communicates with the main return air duct 18 throughwhich return air 34 (whether drawn from the envelope or the cabin) canbe removed from the upper lobe of the body 1.

Return air 34 from the cabin 3 (or the envelope 5) flows through themain return air duct 18P and is supplied to the (conventional) outflowvalve 19. The outflow valve 19 operates in response to control signals Creceived from the control unit 22 to maintain cabin pressurization, ventat least a portion of the return air 34 out of the aircraft as exhaustair 35 and (possibly) supply the remainder of the return air 34 to thecabin air conditioner 20 as recirculate air 36.

The cabin air conditioner 20 may, for example, generally comprise one ormore conventional mixing and filtering units 20 a, and a humiditycontrol unit 20 b, which operates in response to control signals D fromthe control unit 22. In opera the cabin air stream 26 from the airflowcontrol device 13, and recirculate air 36 from the outflow valve 19 arecombined in a mixing unit 20 a, then filtered, cooled (or heated) asrequired, and humidified by the humidity control unit 20 b to createcabin supply air 37. The cabin supply air 37 is then supplied to thecabin through the supply air duct 21.

In the illustrated embodiment, fire suppression is provided by means ofa container of chemical fire suppressant 38 such as, for example Halon(trade name) or an equivalent, connected to the envelope suppler ducts14 and 15 via a valve (or valves) 39 which is responsive to a controlsignal E from the control unit 22. Upon opening the valve 39, chemicalfire suppressant is supplied to the envelope 5 to extinguish the fire.This fire suppressant supply could be from an existing cargo firesuppressant system or it could be added.

If desired, each of the envelope supply ducts 14P, 14S, 15P and 15S canbe provided with its own valve 39, which can be independently controlledby the control unit 22. In this case, chemical fire suppressant 38 canbe drawn from a single, common container, or from separate independentcontainers as desired. This arrangement has the benefit that chemicalfire suppressant can be selectively delivered to any desired quadrant ofthe envelope 5P, 5S, 8P and 8S. Thus smoke/fire detectors can bestrategically distributed within the envelope 5 (for example nearelectrical devices or other potential sources of ignition) so that theapproximate location of a fire can be detected. Upon detection of afire, the flight crew can choose to flood only that portion of theenvelope in which the fire has been detected, thereby conserving firesuppressant and/or facilitating the delivery of higher concentrations offire suppressant to those areas of the envelope 5 where it is mostneeded.

The control unit 22 can suitably be provided as an environment controlpanel within the cockpit of the aircraft. The control unit 22 can bedesigned as a simple switch panel, allowing the flight crew to manuallycontrol the operation of the airflow control device 13, return aircontrol units 17, outflow valve 19 . cabin air conditioner 20 and firesuppressant valve 39. Alternatively the control unit 22 can be at leastpartially automated, such that the operation of the system can becontrolled in accordance with one or more predetermined programs andsignals.

The environment control system of the invention can be incorporate newaircraft construction, or installed as an upgrade or retrofit in anexisting aircraft. Appropriate evaluation of the aircraft mission (e.g.requirements of moisture control, and whether or not air quality controland additionally fire/smoke suppression are required) and testing of therecipient aircraft type (e.g. configuration and geometry) will revealthe numbers, sizing and preferred locations for each of the elements ofthe system, as well as which ones (if any) of the optional elements(e.g. flow blockers, cabin-side nozzles, selectable flow return aircontrol units, humidifiers etc.) are required in order to obtain desiredoperational characteristics. Upgrading an existing aircraft ventilationsystem in accordance with the illustrated embodiment, which incorporatesall optional elements, can be accomplished by the following exemplarysteps:

The cabin liner 7 and the insulation 10 are removed to obtain access tothe envelope 5;

One or more lines of flow blockers 28 are installed on each side;

An anti-corrosion/VOC sorbent material 41 is applied on the metal in theenvelope;

The insulation 10 is refitted as necessary to make a continuous blanketEither new insulation can be used or the existing insulation can bereinstated;

The fire suppressant container 38 (existing or new, if desired) and itscontrol valve(s) 39 are installed;

Upper lobe envelope ventilation supply ducts 14 (and lower lobe envelopeventilation supply ducts 15 if desired) and the associated branch lines16, including shell-side nozzles 27 and (if desired) cabin-side nozzles29 are installed;

A cabin air conditioner (filter, humidifier) is installed andinterconnected. The air conditioner outlet (cabin supply air) isconnected to the existing cabin air ducting, which thereafter functionsas the cabin supply air duct system;

The airflow control device 13 is installed and connected to the mainventilation duct and to the cabin ventilation and envelope ventilationsupply ducts.

Return air control units 17 are installed in the existing return airplenums at the floor level of the cabin envelope 5. Care is required toensure proper sealing around the housings of the return air controlunits 17 so as to minimize leakage;

Return air ducts are installed on both sides of the aircraft andconnected with the return air control units 17 and the existing outflowvalve 19;

The system main control unit 22 is installed in the cockpit andconnected to the airflow control device 13, return air control units 17,outflow valve 19 air conditioner 20 and fire suppression valve 39 inorder to control the various elements of the system. In addition sensorsfor detecting temperature, humidity, smoke(fire) within the cabin andenvelope and optionally an envelope/cabin pressure difference logger areinstalled at desired locations within the cabin and envelope andcorrected to the control unit 22 to provide information in respect ofsystem operation;

If desired, heat exchanger units are installed in the lower lobe andinterconnected with the return air ducts 18, and associated thermostatslocated in the cargo bay(s) 4, so that the cargo bay(s) 4 can be heatedby warm return air 34.

Finally, the cabin liner 7 is reinstalled, with care being taken toclose holes and gaps, so that desired pressures can be maintained withinnormal cabin ventilation air flow rates.

In use the above-described system can provide controlled ventilation ofthe upper lobe envelope 5 and within the cabin 3 in various waysdepending on the flight regime of the aircraft. In the followingexamples, four exemplary modes of operation of the system are described,with reference to FIGS. 3 to 7.

EXAMPLE 1 Normal Cruising Flight

Under normal operation at cruising altitude, the flows of envelope air25 and cabin air 26 are controlled such that the envelope pressure isslightly greater than that of the cabin.

The envelope air 25 supplied to the envelope 5 through the shell-sidenozzles 27 contacts the cold skin 5 and contaminants are removed atleast in part by sorption (e.g., by the anti-corrosion/sorptiontreatment 41), condensation and filtration (e.g. by centrifugal andelectrical forces), and then stored on the interior surface of the skin5 and other cold surfaces within the envelope or as an aerosol. Theextremely low relative humidity of the ventilation air 24 and thus theenvelope air 25 (typically less than approx. 5% at cabin temperatures)means that no significant moisture condensation will accumulate withinthe envelope 5. The envelope air 25 then flows back through theinsulation 10 (as shown by the arrows in FIG. 3), and enters the cabin 3by leakage through the seams 40 between panels of the cabin liner 7.

For example, an envelope pressurization relative to the cabin 3 ofbetween 0.5 and 5 Pa (preferably between approximately 1-2 Pa) and totalenvelope ventilation air 24 injection flows of less than the minimumcabin ventilation rate required for passenger transport aircraft of 0.55lbs per person (which is equivalent to 10 c.f.m. per person at 8,000 ft.cabin pressure altitude) can be maintained for a cabin liner 7 panelingleakage area of less than 73 cm² per person (or, equivalently, 440 cm²per six passenger row). For a 5 c.f.m. per person envelope air flowrate, and a stack pressure of 2 Pa, the leakage area per six passengerrow can be up to 100 cm². For a leakage area of 440 cm², moisturediffusion from the cabin to the envelope through typical panel openingsis less than 5 mg/s per row (crack length) at a cabin humidity of 60%.At this rate a 30 row 180 passenger plane would accumulate a maximum ofabout 1 pound of moisture during a three hour flight. Actually, it willbe negligible because convective transfer from the envelope to the cabinwill offset upstream or back diffusion.

To achieve the allowable leakage areas, the integrity (i.e. minimizedleakage area) of the cabin liner 7 paneling must be maintainedthroughout and any openings at the overhead compartment must be sealed.With this degree of sealing, during a sudden aircraft depressurizationevent (for example, if a cargo door opens in flight), one or more panelsof the cabin liner 7 will “pop” to equalize the pressure differencebetween the cabin 3 and the envelope 5. Additionally, the damper 33 ofthe return air control units 17 can be designed so that both theenvelope opening 31 and the cabin opening 32 will open automatically ina sudden depressurization event. When insulation continuity ismaintained, envelope air 25 entering the cabin 3 from behind theinsulation 10 will be warmed by dynamic insulation heat recovery as itpasses through insulation gaps.

As shown in FIG. 3 During normal flight at cruising altitude, envelopeair 25 is injected behind and/or in front of the insulation 10, and thecabin recirculation system is operating (that is, cabin supply air 37made up of cabin air 26 and recirculate air 36 are being supplied to thecabin 3 via the cabin air conditioner 20). The return air control units17 are set so that return air 34 is drawn from the cabin 3. In thismode, the cabin air conditioner 20 can be operated to maintain cabinrelative humidity levels in excess of 20% (preferably between 40 and50%). Moisture condensation within the envelope 5 from humid cabin airis prevented by the relative pressurization of the envelope 5, and theenvelope is kept dry. Furthermore, contaminant gases and particleswithin the envelope air 25 are removed in part prior to entering thecabin 3 by sorption and condensation, and physical filtering as itpasses back through the insulation 1, thereby improving cabin airquality over that typically encountered in conventional aircraft.

Return air 34 is drawn from the cabin 3 through the return air controlunit(s) 17 and the main return air duct 18. If desired, this return air34 can be used to heat the lower lobe through the use of one or moreheat exchangers (not shown).

The outlet valve 19 operates to vent a portion of the return air 34 outof the aircraft as exhaust air 35 and supplies the remainder asrecirculate air 36 to the cabin air conditioner 20.

EXAMPLE 2 Taxi and Ascent

FIG. 4 illustrates system operation during taxi and ascent to cruisingaltitude. Conventionally, the cabin pressure is maintained to analtitude equivalent of approximately 8000 ft. which means that the cabinpressure during the cruise phase of flight will be approximatelythree-quarters of sea level pressure. Thus during the initial portion ofascent, the cabin depressurizes, and approximately one quarter of theair in the envelope 5 at take-off would normally tend to bleed into thecabin 3. During this period, the envelope 5 will be relatively warm incomparison to cruising altitude temperatures, and VOCs sorbed andcondensed in the envelope may volatilize. The airflow control device 13is operated to pressurize the cabin relative to the envelope. At thesame time, the return air control units 17 are controlled to draw returnair 34 from the envelope 5, and the outflow valve 19 vents all of thereturn air 34 out of the aircraft as exhaust air 35. This operationeffectively purges VOC contaminants (chemical and microbial, if any)within the envelope 5, and prevents them from entering the cabin 3. In aconventional aircraft ventilation system, these contaminants wouldnormally be drawn into the cabin during ascent.

EXAMPLE 3 Descent and Taxi

FIG. 5 illustrates system operation during descent from cruisingaltitude as the cabin pressurizes, and taxi after landing. During thisperiod the envelope is comparatively cold relative to the outsidetemperatures, and injection of air into the envelope during this phaseof flight would cause accumulation of moisture condensation.Accordingly, for descent and taxi, the airflow control device 13operates to divert all ventilation air 24 into the cabin air conditioner20, and the return air control units 17 draw return air 34 from thecabin 3, thereby effectively isolating the envelope 5. The outflow valve19 can be operated to vent all of the return air 34 as exhaust 35 orrecycle some of the return air 34 back to the cabin air conditioner 20as desired.

EXAMPLE 4 Ground Purging

Operation of the environment control system of the invention during taxiand ascent (Example 2 above) is effective in purging VOCs from theenvelope 5. However, in some cases it may be considered good practice toperform additional purging of the upper lobe envelope 5 as well as thelower lobe envelope 8 while the aircraft is parked (such as, forexample, between flights). In this case, ventilation air 24 can beprovided by a conventional round conditioned air supply unit 42connected to the two upper lobe ventilation air ducts 14 upstream of theairflow control device 13, as shown in FIG. 6, and to the two lower lobeducts 15. The airflow control device 13 directs ventilation air 24 intothe envelope 5 via branch ducts 16 as envelope air 25, in order tovolatilize VOCs adsorbing within the envelope 5 and to remove moisture.The ground conditioned air supply unit 42 is also connected to the lowerlobe supply ducts 15 and branch ducts 16 to vent any moisture in thisportion of the envelope. In order to accelerate this process, it may bedesirable to operate the conditioned air supply unit 42 so as to heatthe ventilation air 24 or use engine bleed air. The return air controlunits 17 are set to draw return air 34 from the envelope 5, and theoutflow valve 19 vents all of the return air 34 out of the aircraft asexhaust 35.

This operation will remove moisture and air contaminant accumulation, ifpresent, in the upper and lower lobe envelopes.

EXAMPLE 5 In-flight Fire and/or Pyrolysis

FIG. 7 illustrates the air handling system operation during an in-flightfire event in the envelope. When smoke (or combustion products)indicative of a fire is detected, the airflow control device 13 is setto divert all ventilation air 24 to the cabin air conditioner 20. At thesame time, the return air control units 17 are set to draw return air 34from the envelope 5, and the outflow valve 19 operates to vent all ofthe (smoke-laden) return air 34 out of the aircraft as exhaust air 35.Diversion of the ventilation air 24 to the cabin air conditioner 20(with the cabin air conditioner 20 on) allows the cabin 3 to bepressurized relative to the envelope 5, and thereby prevent infiltrationof smoke and combustion products into the cabin 3 if the fire is in theenvelope 5. At that stage, fire suppressant can be injected into theenvelope (either the entire envelope 5 can be flooded with firesuppressant, or, alternatively, the fire suppressant may be directedinto a selected quadrant of the envelope). Maintaining a positive cabinpressure relative to the envelope ensures that smoke, fire suppressant,and combustion products are substantially prevented from entering thecabin, thereby providing effective separation of passengers from noxiousgases.

If desired, however, the cabin air conditioner 20 can be turned off tostop the flow of ventilation air 24 into the cabin 3, after injection offire suppressant into the envelope 5. This can be used to reduce thesupply of oxygen available to the fire, but at the expense of allowingcombustion products to leak into the cabin 3.

Alternatively, if the fire is in the lower lobe envelope, then firesuppressant can be injected into that portion of the envelope usingducts 15 and 16. This system has the advantage over current firesuppression systems of not exposing animals, if present, to the healthand safety hazards of fire suppressants and their combustion products incombination with fire and smoke.

The above detailed description and examples describe a preferredembodiment of the present invention, in which ventilation air may beindependently supplied to each of four quadrants of the envelope 5;shell-side and cabin-side nozzles 27, 29 are respectively used to injectventilation air behind and in front of the insulation blankets 10;envelope air flows due to stack effects are restricted by the use offlow blockers 28; chemical fire suppressants can be selectively injectedinto the envelope 5; and means are provided for on-the-ground purgingthe envelope 5 by the use of a ground conditioned air supply unitconnected to the ventilation air inlet ducts. However, the skilledartisan will recognize that these features can be used in any desiredcombination, depending on the design and mission of the particularaircraft in question.

For example, the skilled artisan will appreciate that the envelope 5need not necessarily be divided into four quadrants, each of which areserved by independent ventilation supply systems. It is not necessary todivide the envelope 5 into upper and lower lobes, if such a division isnot desired by the aircraft designer. If desired, the envelope airstream 25, can be divided into upper and lower lobe supply streams, oralternatively both lobes of the envelope 5 can be ventilated using acommon envelope air stream 25. Similarly, it is possible to utilizeshell-side nozzles 27 alone; or cabin-side nozzles 29 alone; orshell-side nozzles 27 in one area of the envelope 5, and cabin-sidenozzles 29 in another area of the envelope 5, all as deemed appropriateby the designer.

Similarly, the skilled artisan will appreciate that the envelope 5 neednot necessarily be divided into upper and lower, port and starboardquadrants. In practice, it is possible to divide the envelope 5 asrequired to provide a localized ventilation regime appropriate to aspecific portion of the envelope 5. For example, it may be desirable toprovide a ventilation regime in the crown portion of the envelope 5(e.g. to eliminate “rain-in-the-plane” phenomenon) which differs fromthat provided in the sides of the envelope 5. Division of the envelope 5in this manner can readily be accomplished by means of the presentinvention.

Furthermore, the skilled artisan, will also recognize that, just as theenvelope 5 can be divided radially into quadrants, it is also possibleto divide the envelope 5 longitudinally into sections, such as, forexample, by means of suitable flow blockers 28 circumferentiallydisposed between the cabin liner 7 and the shell 6. Each longitudinalsection may also be provided with independent envelope and cabin airstreams 25, 26, and may also include its own set of return air controlunits 17, and return air ducts 34 etc. to thereby allow envelopeventilation control independent of other sections of the envelope 5. Forexample, it may be desirable to provide independently controllableenvelope/cabin ventilation (e.g. in terms of air pressures and flowrates) in the cockpit and passenger cabin. Furthermore, within thepassenger cabin, in may be desirable to have differing envelopeventilation regimes within passenger seating and food preparation areas.This can be accomplished by longitudinally dividing the envelope 5 intoappropriate sections, and providing envelope and cabin ventilation airducts 14, 21, appropriate cabin and/or shell-side nozzles 27, 29, andreturn air control units 17 etc. as required to provide the desiredventilation regime within each section. Longitudinal division of theenvelope 5 also creates a further mode of operation of the system of thepresent invention during a fire or pyrolysis event. In particular, in acase of smoke in the cockpit, it would be possible to controlventilation regimes in all of the sections of the envelope 5 to delivermaximum air flow to the cockpit (perhaps with reduced ventilation airflow to the passenger cabin), and thereby more effectively purge smokeand combustion products from the cockpit area.

In the illustrated embodiment, the return air control unit 17 and cabinair inlet 32 are located in the envelope space 5 near the floor 2 of thecabin. However, it will be appreciated that these components may equallybe located elsewhere as deemed appropriate by the aircraft designer.Similarly, the locations or the envelope ventilation supply ducts 14,15, the return air ducts 18 and the cabin ventilation supply duct 21 canbe varied as deemed appropriate by the designer.

The ability of the system of the invention to pressurize the cabinrelative to the envelope, or vise-versa, is inherent to the presentinvention, and may be utilized to achieve any of the operating modes (interms of envelope and cabin ventilation, and return air recirculationand venting) described in the above examples. However, it will beapparent that one or more of the operating modes may be omitted, if suchmode of operation is unnecessary for the mission and/or design of anyparticular aircraft. For example, in some aircraft, it may be desirableor necessary to omit operating modes in which the cabin is pressurizedrelative to the envelope. In such circumstances, all return air may bedrawn from the cabin exclusively, in which case the return air controlunit 17 may be replaced by a simple fixed return air inlet incommunication with the return air ducts 18.

It is considered that the use of flow blockers 28 will reduce naturalconvective (stack-effect) air flows within the envelope, and that thiswould likely have the effect of reducing moisture condensation withinthe envelope, even in the absence of envelope pressurization. Thecapability of the system of the present invention to pressurize theenvelope with dry ventilation air will serve to virtually eliminatemoisture condensation within the envelope, at least during the cruiseportion of the flight cycle. The skilled artisan, will appreciate thatflow blockers 28 may be used independently of the other elements of theinvention described herein. Thus the skilled artisan will recognize thatflow blockers 28 could be incorporated into an aircraft, even in theabsence of an envelope ventilation system. Similarly, an envelopeventilation system may be used either in conjunction with, or without,flow blockers 28.

Thus it will be appreciated that the above description of a preferredembodiment is intended to describe various elements, which may be usedalone or in any desired combination as desired to achieve as appropriateto the particular circumstances. It will therefore be understood thatthe above-described preferred embodiment is intended to be illustrative,rather than limitative of the present invention, the scope of which isdelimited solely by the appended claims.

What is claimed is:
 1. An environment control system installed in thebody of an aircraft having a body shell enclosing an inner space, aliner disposed within the inner space and defining an envelope spacebetween the liner and the body shell and an interior space on the otherside of the liner, an air supply for providing a flow of dry ventilationair to the inner space of the body, an envelope air distribution systemfor directing air from the air supply into the envelope space, a returnair control unit capable of drawing return air from the interior space,and an air flow controller which controls the flow of air into theenvelope space to develop a sufficient pressure in the envelope spacerelative to the pressure in the interior space to substantially preventthe flow of air from the interior space into the envelope space causedby stack pressure across the liner between the envelope space and theinterior space which tends to cause air to flow across the liner fromthe interior space into the envelope space.
 2. An environment controlsystem as claimed in claim 1, further comprising means for directing aflow of ventilation air from said air supply into said interior space.3. An environment control system as claimed in claim 1, wherein theenvelope air distribution system comprises at least one envelope supplyduct disposed longitudinally in the aircraft body and at least onerespective ventilation air branch line disposed within said envelopespace for feeding ventilation air from said supply duct into saidenvelope space.
 4. An environment control system as claimed in claim 3,wherein each ventilation air branch line includes at least one nozzlefor injecting ventilation air into the envelope space.
 5. An environmentcontrol system as defined in claim 4, wherein at least one nozzle is ashell-side nozzle capable of injecting envelope space ventilation airbetween an insulation jacket disposed in said envelope space, and saidbody shell.
 6. An environment control system as defined in claim 5,wherein two or more shell-side nozzles are provided in communicationwith each ventilation branch line, the shell-side nozzles being disposedat spaced intervals around a circumference of the envelope space.
 7. Anenvironment control system as defined in claim 6, wherein at least onenozzle is an interior space-side nozzle capable of injecting envelopeventilation air between an insulation jacket and the liner.
 8. Anenvironment control system as defined in claim 7, wherein two or moreinterior space-side nozzles are provided in communication with eachventilation branch line, the interior space-side nozzles being disposedat spaced intervals around the circumference of the envelope space. 9.An environment control system as defined in claim 1, wherein ananti-corrosion/volatile organic compound sorption treatment is appliedto an interior surface of the aircraft structure possibly exposed tocondensation.
 10. An environment control system as defined in claim 9,wherein the anti-corrosion/volatile organic compound sorption treatmentis formulated to provide acceptable characteristics of: adhesion tometal surfaces; hydrophobic; low flammability; and low off-gassing attypical envelope space temperatures during cruising flight.
 11. Anenvironment control system as defined in claim 10, wherein theanti-corrosion/volatile organic compound sorption treatment isformulated to: resist solidification within the aircraft envelope space;sorb ventilation air volatile organic compound at typical envelope spacetemperatures during cruising flight and desorb said ventilation airvolatile organic compounds at warmer temperatures substantially withouthysteresis.
 12. An environment control system as defined in claim 1,wherein the return air control unit is adapted to draw the return airstream from the interior space only.
 13. An environment control systemas defined in claim 12, wherein the return air control unit comprises ahousing, an envelope opening defined in the housing and in communicationwith the envelope, an interior space opening defined in the housing andin communication with the interior space, and a damper capable ofselectively closing the envelope opening and the interior space opening.14. An environment control system as defined in claim 1, wherein theliner has a leakage area such that the flow of air into the envelopespace required to develope a pressure in said envelope space required todevelope a pressure in the interior space is less than 10cfm peroccupant seat.
 15. An environment control system as defined in claim 1,further comprising air flow barriers disposed within the envelope spaceand which divide the envelope space into a plurality of envelope spacesections, and ventilation means capable of supplying ventilation airfrom said distribution system to an envelope space section at a flowrate which is different from the flow rate of air to another envelopespace section.
 16. An environment control system as claime in claim 15,wherein said ventilation means includes ventilation to each envelopespace section.
 17. An environment control system as defined in claim 16,wherein a flow blocker is disposed within the envelope space atapproximately mid-height of an upper lobe of the body of the aircraft.18. An environment control system as defined in claim 2, wherein theinterior space air distribution system comprises: an air conditionercommunicating with the air supply for receiving interior ventilation airfor the interior space and operative to condition the interior spaceventilation air to create supply air for the interior space; and asupply air duct capable of directing the interior space supply air intothe interior space.
 19. An environment control system as defined inclaim 18, wherein the air conditioner is operative to maintain arelative humidity of the cabin supply air of at least 20%.
 20. Anenvironment control system as defined in claim 19, wherein the airconditioner is operative to maintain a relative humidity of the cabinsupply air of between 20% and 80%.
 21. An environment control system asdefined in claim 20, wherein the air conditioner is operative tomaintain a relative humidity of the cabin supply air of between 40% and70%.
 22. An environment control system as defined in claim 16, whereineach envelope section has a respective duct for enabling air to be drawntherefrom, and further including a controller for controlling the flowof air from an envelope space section independently of another envelopespace section.
 23. An environment control system as defined in claim 15,further comprising an insulation jacket disposed within said envelopespace and wherein the ventilation means for at least one envelope spacesection includes a ventilation outlet port between said jacket and saidshell.
 24. An environment control system as defined in claim 15, furthercomprising an insulation jacket disposed in said envelope space, andwherein said envelope space for at least one envelope space sectionincludes a ventilation outlet port disposed between said insulationjacket and said liner.
 25. An environment control system as defined inclaim 1, wherein said air supply is provided from an engine of saidaircraft, and said control system comprises a first air conditioner forcontrolling the temperature of the air from said engine and forsupplying said air to said envelope air distribution system, a secondair conditioner for receiving air supplied from an engine of saidaircraft and for conditioning the temperature of said air, and airfeeding means for feeding the air from said second air conditioner intosaid interior space.
 26. An environment control system as defined inclaim 1, wherein the interior space includes at least one floor defininga cabin space above said floor, and said system further comprises flowbarrier means, including a flow blocker, disposed in said envelope spaceat a level different than the level of the or each cabin space floor,and defining an upper envelope space above said flow blocker and a lowerenvelope space below said flow blocker, wherein said flow barrier meansis arranged to substantially prevent air which resides in the upper andlower envelope spaces from flowing between said upper envelope space andsaid lower envelope space, through the space between said body shell andsaid liner, thereby to reduce stack pressure across said liner.
 27. Anenvironment control system as claimed in claim 26, wherein insulation isdisposed in said envelope space, and said flow blocker is disposedbetween at least one of said liner and said insulation and said bodyshell and said insulation.
 28. An environment control system as definedin claim 27, wherein the envelope air distribution system comprises atleast one nozzle capable of injecting at least a portion of the envelopeventilation air steam into a portion of the envelope below said flowblocker, and at least one nozzle capable of injecting at least a portionof the envelope above said flow blocker.
 29. The method of claim 26,further comprising the step of humidifying the interior spaceventilation air prior air supplying the same to the interior space. 30.The method of claim 26, further comprising the steps of venting aportion of the return air stream out of the aircraft and recirculating aremaining portion of the return air stream back into the interior space.31. A method as claimed in claim 26, wherein the surface of the bodyshell within the envelope space has an anti-corrosion/volatile organiccompound sorption treatment applied thereto and the step of supplyingenvelope space ventilation air to the envelope space includes directingthe ventilation air at the anti-corrosion/volatile organic compoundtreatment on the inside surface of said body shell.
 32. A method asclaimed in claim 26, wherein the step of supplying envelope spaceventilation air to the envelope space comprises the step of passing saidventilation air through at least one nozzle.
 33. A method of controllingthe environment within an aircraft body having a body shell enclosing aninner space, a liner disposed within the inner space and defining anenvelope space between the liner and the body shell and an interiorspace on the other side of the liner, the method comprising: a)providing a flow of dry ventilation air; b) dividing the flow ofventilation air into an envelope space ventilation air stream and aninterior space ventilation air stream; c) supplying the envelope spaceventilation air to the envelope space; d) supplying the interior spaceventilation air to the interior space; e) drawing a return air streamfrom the interior space; and f) controlling the envelope spaceventilation air stream and the interior space ventilation air stream todevelop a sufficient pressure in the envelope space relative to thepressure in the interior space to substantially prevent the flow of airfrom the interior space into the envelope space caused by stack pressureacross the liner between the envelope space and the interior space whichtends to cause air to flow across the liner from the interior space intothe envelope space.
 34. The method of claim 33, further comprising thestep of injecting at least a portion of the envelope ventilation airinto a space between said body shell and an insulation jacket disposedbetween said liner and said body shell.
 35. The method of claim 33,further comprising the step of injecting at least a portion of theenvelope ventilation air into a space between an insulation jacket,disposed in said envelope space, and said liner.
 36. The method of claim33, further comprising the step of humidifying the interior spaceventilation air prior to supplying the same to the interior space. 37.The method of claim 33, further comprising the steps of venting aportion of the return air stream out of the aircraft and recirculating aremaining portion of the return air stream back into the interior space.38. A method as claimed in claim 33, wherein the surface of the bodyshell within the envelope space has an anti-corrosion/volatile organiccompound sorption treatment applied thereto and the step of supplyingenvelope space ventilation air to the envelope space includes directingthe ventilation air at the anti-corrosion/volatile organic compoundtreatment on the inside surface of said body shell.
 39. A method asclaimed in claim 33, wherein the step of supplying envelope spaceventilation air to the envelope space comprises the step of passing saidventilation air through at least one nozzle.
 40. A method as claimed inclaim 33, further comprising the step of providing a flow blocker in theenvelope space at a level other than the level of a floor of theinterior space and defining an upper envelope space above said flowblocker and a lower envelope space below said flow blocker, wherein saidflow blocker is arranged to sunstantially prevent air which resides inthe upper and lower envelope spaces from flowing between said upperenvelope space and said lower envelope space through the space betweensaid body shell and said liner, thereby to reduce stack pressure acrosssaid liner.
 41. An environment control system installed in the body ofan aircraft, the aircraft having a body shell enclosing an inner space,a liner disposed within the inner space and defining an envelope spacebetween the liner and the body shell, and an interior space on the otherside of the liner, the interior space including at least one floordefining a cabin space above said floor, the environment control systemcomprising flow barrier means, including a flow blocker, disposed insaid envelope space at a level different than the level of the or eachcabin space floor and defining an upper enbelope space above said flowblocker and a lower envelope space below said flow blocker, wherein saidflow barrier means is arranged to substantially prevent air whichresides in the upper and lower envelope spaces from flowing between saidupper envelope space and said lower envelope space through the spacebetween said body shell and said liner, thereby to reduce stack pressureacross said liner.
 42. An environment control system as claimed in claim41, comprising insulation disposed in said envelope space, and whereinsaid flow blocker is disposed between at least one of said liner andsaid insulation and said body shell and said insulation.
 43. Anenvironment control system as claimed in claim 42, wherein said flowblocker is arranged to compress said insulation towards said body shell.44. An environment control system as claimed in claim 41, wherein saidflow blocker is positioned at about mid-height of said envelope spaceabove said floor level.
 45. An environment control system as claimed inclaim 41, comprising at least one said flow barrier means disposedwithin the envelope space on each side of said aircraft.
 46. Anenviroment control system as claimed in claim 45, comprising a pluralityof said flow barrier means disposed within said envelope space on eachside of said aircraft, and being spaced from one another about thecircumference of said envelope space.
 47. An environment control systemas claimed in claim 41, further comprising an air supply for providing aflow of dry ventilation air to the inner space of the body, an envelopeair distribution system for directing air from the air supply into theenvelope space and wherein the envelope air distribution system includesat least one outlet port for injecting envelope ventilation air intosaid upper envelope ventilation air into the lower envelope space. 48.An environment control system installed in the body of an aircrafthaving a body shell enclosing an inner space, a linear disposed withinthe inner space and defining an envelope space between the linear bodyshell, and an interior space on the other side of the linear, an airsupply for providing a flow of dry ventilation air into the inner paceof the body, air feeding means for feeding a flow of air from the airsupply into the envelope space, and wherein the linear has a leaskagearea such that the flow of air into the envelope space required todevelope a pressure in the envelope space of at least 0.5Pa above thepressure in the interior space is less than 10cfm per occupant seat. 49.An environment control system as claimed in claim 48, wherein theinterior space includes a cabin space for accomodating people and havinga cabin space floor, the environment control system further comprisingflow barrier means, including a flow blocker, disposed in said envelopespace above the level of said cabin space floor and defining an upperenvelope space above said flow blocker and a lower envelope space belowsaid flow blocker, wherein said flow barrier means is arranged tosubstantially prevent air which resides in the upper and lower envelopespaces from flowing between said upper envelope space and said lowerenvelope space through the space between said body shell and saidlinear, thereby to reduce stack pressure across said linear.
 50. Anenvironment control system installed in the body of an aircraft, theaircraft having a body shell enclosing an inner space, a linear disposedwithin the inner space and defining an envelope space between the linerand body shell and an interior space on the other side of the liner, andinsulation disposed within said envelope space, the control systemcomprising an air supply for providing a supply of air from an engine ofsaid aircraft to the inner space of the body, an envelope airdistribution system for directing air into the envelope space, saiddistribution system comprising at least one envelope supply duct forfeeding air along said aircraft body and at least one ventilation airbranch line disposed within said envelope space for feeding ventilationair from said supply duct into said envelope space between said linearand said insulation, a first air conditioner for controlling thetemperature of the air from said engine and for supplying said air tosaid distribution system, a second air conditioner for receiving airsupplied from an engine of said aircraft and for conditioning thetemperature of said air, and air feeding means for feeding the air fromsaid second air conditioner into said interior space.
 51. An environmentcontrol system as claimed in claim 50, further comprising means forfeeding air from said first air conditioner to said second airconditioner.
 52. An environment control system as claimed in claim 51,comprising an air flow controller for controlling the flow of air fromsaid first air conditioner to said second air conditioner.
 53. Anenvironment control system as claimed in claim 50, further comprising anair flow controller for controlling the flow of air from said first airconditioner to said air distribution system.
 54. An environment controlsystem as claimed in claim 50, further comprising a return air controlunit capable of drawing return air from the interior space.
 55. Anenvironment control system as claimed in claim 54, further comprising amixing unit for mixing air supplied from said engine and from saidreturn air control unit, and supplying the mixed air to said interiorspace.
 56. An environment control system as claimed in claim 50, furthercomprising a return air control unit capable of drawing air from saidenvelope space.
 57. An environment control system as claimed in claim50, further including air flow barriers disposed within the envelopespace and which divide the envelope space into a plurality of envelopespace sections, and ventilation means capable of supplying ventilationair from said distribution system to an envelope space section at a flowrate which is different from the flow rate of air to another envelopespace section.
 58. An environment control system as claimed in claim 57,including ventilation control means for independently controlling theventillation to each envelope space section.
 59. An environment controlsystem as claimed in claim 57, further comprising an insulation jacketdisposed within said envelope space, and wherein said ventilation systemincludes a ventilation outlet port for at least one envelope spacesection disposed between said insulation jacket and said shell.
 60. Anenvironment control system as claimed in claim 57, further comprising aninsulation jacket disposed within said envelope space, and wherein saiddistribution system includes a ventilation outlet port for at least oneenvelope space section disposed between said insulation jacket and saidliner.
 61. An environment control system as claimed in claim 50, whereinthe liner has a leakage area such that the flow of air into the envelopespace required to develope a pressure in said envelope space of at least0.5Pa above the pressure in the interior space is less than 10cfm peroccupant seat.
 62. An environment control system installed in the bodyof an aircraft, the aircraft having a body shell enclosing an innerspace, a liner disposed within the inner space and defining an envelopespace between the liner and the body shell, and an interior space on theother side of the liner, the control system comprising: an envelopeexhaust controller arranged for receiving gas directly from saidenvelope space and expelling said gas from said aircraft, and controlmeans for controlling the pressure of gas in said inner space tomaintain the pressure of said envelope space below that of said interiorspace.
 63. An environment control system as claimed in claim 62, furthercomprising an air supply for providing a flow of air to the inner spaceof the body, means for directing a flow of ventilation air from said airsupply into said interior space, and wherein said control means includesan air flow controller for controlling the flow of air into saidinterior space to maintain the pressure in the interior space above thatof the envelope space.
 64. An environment control system as claimed inclaim 62, wherein said envelope exhaust controller includes a pluralityof envelope exhaust ports spaced apart in a direction along the lengthof said envelope space.
 65. An environment control system as claimed inclaim 64, wherein said envelope exhaust controller further comprises aplurality of valves, each for controlling the flow ofn gas from arespective envelope exhaust port.
 66. An environment control system asclaimed in claim 62, further comprising air flow barriers disposedwithin the envelope space and which divide the envelope space into aplurality of envelope space sections, each section having an exhaustoutlet port, and wherein said envelope exhaust controller is capable ofcontrolling the flow of gas drawn from an envelope space sectionindependently of another envelope space section.
 67. An environmentcontrol system as claimed in claim 62, further comprising a firesuppression system for releasing a flow of fire suppressant into theenvelope space.
 68. An environment control system as claimed in claim67, further comprising an air supply for providing a flow of dryventilation air into the inner space, an envelope air distributionsystem for directing air from the air supply into the envelope space,and wherein the fire suppression system is connected to said envelopeair distribution system for introducing fire suppressant into saiddistribution system.
 69. An environment control system as claimed inclaim 68, wherein said fire suppressant system comprises a container offire suppressant and a valve operable to introduce fire suppressant fromsaid container into said envelope air distribution system.
 70. Anenvironment control system as claimed in claim 67, wherein the firstsuppressant comprises any one or more of Halon, carbon dioxide,nitrogen, and other fire suppressant agents, or mixtures of these. 71.An environment control system as claimed in claim 62, wherein ananti-corrosion/volatile organic compound absorption treatment is appliedto an interior surface of the aircraft structure possibly exposed tocondensation.
 72. An environment control system as claimed in claim 71,wherein the anti-corrosion/VOC sorption treatment is formulated toprovide acceptable characteristics of: adhesion to metal surfaces;hydrophobic; low flammability; and low off-gassing at typical and belowtemperatures during cruising flight.
 73. An environment control systemas claimed in claim 71, wherein the anti-corrosion/VOC sorptiontreatment is formulated to: resist solidification within the aircraftenvelope; sorb ventilation air VOCS at typical envelope temperaturesduring cruising flight and de-sorb said ventilation air VOCS at warmertemperatures substantially without hysterics.
 74. The method ofcontrolling the environment within an aircraft body, the body having abody shell enclosing an inner space, a liner disposed within the innerspace and defining an envelope space between the liner and the bodyshell, and an interior space on the other side of the liner, an envelopeexhaust duct for drawing gas directly from the envelope space andexhausting said gas from said aircraft, the method comprising the stepsof: drawing gas directly from said envelope space through said duct andexhausting the gas drawn through said duct directly from said aircraft,and controlling the pressure of gas in the liner space such that thepressure in the envelope space is below that of the interior space. 75.A method as claimed in claim 74, further comprising providing a flow ofdry ventilation air into the interior space and controlling the pressureof air in said inner space such that the pressure of air in saidinterior space is greater than the pressure or air in said envelopespace.
 76. A method according to claim 74, further comprising supplyingventilation air to said envelope space.
 77. A method according to claim74, comprising performing the step of drawing gas from said envelopespace when the aircraft is either on the ground, during the period ofaircraft ascent to cruising altitude, or detecting smoke or fire in theenvelope space and/or when injecting fire suppressant into the envelopespace.